Many different complex sounds, including speech and music, have acoustic waveforms that possess some form of temporal periodicity, and pitch is a fundamental human perception closely related to this temporal periodicity. We propose to address issues concerned with the temporal processing of complex sounds, primarily complex tones and iterated rippled noises, as related to pitch perception. A variety of attributes are associated with the perception of pitch, and we propose to address issues concerned with four specific perceptual attributes, namely, matched pitch, spectral dominance, pitch strength and phase effects. The major goal is to understand the neural basis of pitch perception in humans. We propose to use a multidisciplinary approach based on animal psychophysics and neurophysiology in order to gain insights into the temporal mechanisms underlying pitch perception. In animal psychophysical experiments, the perceptual capabilities of the chinchilla for processing the same types of complex sounds used in human psychophysical experiments will be evaluated. The goal of these behavioral experiments is to determine if the underlying neural mechanisms responsible for the perception of complex pitch in human subjects are unique or special to the human nervous system, or whether these are common neural mechanisms that exist across mammals. In physiological experiments, the neural representations of the temporal features of the same complex sounds used in the human and chinchilla behavioral experiments will be studied at the first level of auditory processing, namely, the cochlear nucleus. The goal of the physiological experiments is to understand how information about waveform and envelope periodicities is represented and processed in each of the various principal subsystems in the cochlear nucleus. The comparisons between neurophysiological data and behavioral data from the chinchilla with human psychophysical and perceptual data will provide an important biological context in which to understand the basis of human pitch perception.